Wallerian degeneration and regeneration process.

1. WALLERIAN DEGENERATION
AND REGENERATION
PRESENTED BY:
DR. LAKSHMI PAVANI P. (PT)

2. CONTENTS
 INTRODUCTION
 CLASSIFICATION OF NERVE INJURIES
 INJURY OF THE NERVE CELL BODY
 INJURY OF THE NERVE CELL PROCESS
 CHANGES IN THE DISTAL SEGMENT OF THE AXON
 CHANGES IN THE PROXIMAL SEGMENT OF THE AXON
 CHANGES IN THE NERVE CELL BODY
 RECOVERY OF THE NEURONS FOLLOWING INJURY
 REGENERATION OF AXONS IN THE PERIPHERAL NERVES
 REGENERATION OF AXONS IN THE CNS
WALLERIAN
DEGENERATION
REGENERATION

3. INTRODUCTION
 Neuron is the basic functional unit of the nervous system.
 In the mature human, if it is destroyed, it is not replaced.
 It may be injured due to various reasons(cutting, crushing, pull & pressure).
 These injuries may damage a nerve variously & the injury is classified according to the
extent of the damage.

7. SEDDON’S CLASSIFICATION OF NERVE
INJURY
 Seddon (1944) described 3 clinical types of nerve injury:
Neurapraxia (class I)
 The term applied to a transient block
 Paralysis is incomplete, recovery is rapid & complete, & there is no nerve degeneration
 Pressure is the most common cause

8. Axonotmesis (class II)
 The term applied to a nerve lesion in which the axons are damaged but the surrounding
connective tissue sheaths remain intact
 Wallerian degeneration occurs peripherally
 Functional recovery is more rapid & more complete than after complete section of the
nerve trunk
 Crush injuries, traction, & compression are the most common causes

9. Neurotmesis (class III)
 The term applied to complete section of the nerve trunk
 Occur on severe contusion, stretch, laceration
 Surgical repair is required.

10. SUNDERLAND’S CLASSIFICATION
 Sunderland (1951) expanded seddon’s classification to 5 degrees:
First-degree (class I) : seddon’s neurapraxia & first-degree are the same
Second-degree (class II) : seddon’s axonotmesis & second-degree are the same
Third-degree (class II):
 Nerve fiber interruption
 There is a lesion of the endoneurium, but the epineurium & perineurium remain intact
 Recovery from a third-degree injury is possible, but surgical intervention may be required

11. Fourth-degree (class II):
 Only the epineurium remain intact
 Surgical repair is required
Fifth-degree (class III):
 seddon’s neurotmesis
 Lesion of complete transection of the nerve
 Recovery is not possible without an appropriate surgical treatment

13. INJURY OF THE NERVE CELL BODY
 Severe damage of the nerve cell body may result in degeneration of the entire neuron.
 In the CNS, the tissue macrophages (microglial cells) remove the debris, & the
neighboring astrocytes replace the neuron with scar tissue
 In the PNS, the tissue macrophages remove the debris, & the local fibroblasts replace the
neuron with scar tissue

14. INJURY OF THE NERVE CELL PROCESS
 If the axon of the nerve cell is divided, degenerative changes will take place in
1. Distal segment of the axon
2. A portion of the axon proximal to the injury
3. The cell body from which the axon arises

15. CHANGES IN THE DISTAL SEGMENT OF
THE AXON
 Wallerian degeneration is the changes that occur distally to the site of damage on an axon
 Axon becomes swollen & irregular; the axon is broken into fragments, & the debris is
digested by surrounding schwann cells & tissue macrophages
 Entire axon is destroyed within a week
 Myelin sheath is converted into lipid droplets
 The droplets are extruded from the schwann cell & subsequently are phagocytosed by
tissue macrophages

16.  Schwann cells now begin to proliferate rapidly & axonal sprouts grow from the proximal
stump, enter the distal stump, & grow toward the nerve's end-organs
 If regeneration does not occur, the axon & the Schwann cells are replaced by fibrous
tissue produced by local fibroblasts

18. CHANGES IN THE PROXIMAL SEGMENT
OF THE AXON
 The changes in the proximal segment of the axon are similar to those that take place in the
distal segment but extend only proximally above the lesion as far as the first node of
ranvier

19. CHANGES IN THE NERVE CELL BODY
 The changes that occur in the cell body following injury to its axon are referred to as
retrograde degeneration
 The nissil material becomes fine, granular, & dispersed throughout the cytoplasm
(chromatolysis)
 The nucleus moves toward the periphery of the cell, & the cell body swells & becomes
rounded
 Synaptic terminals are replaced by schwann cells in the PNS & microglial cells or
astrocytes in the CNS

20. RECOVERY OF NEURONS FOLLOWING
INJURY
 The recovery of the nerve cell body & regeneration of its processes may take several
months.
 RNA & protein synthesis is accelerated
 A reconstitution of the original nissil structure
 A decrease in the swelling of the cell body
 A return of nucleus to its characteristic central position

21. REGENERATION OF AXONS IN
PERIPHERAL NERVES
 Depend on endoneurial tubes & possessed by schwann cells
 The following mechanisms are involved:
1. The axons are attracted by chemotropic factors secreted by the schwann cells in the distal
stump.
2. Growth-stimulating factors exist within the distal stump, &
3. Inhibitory factors are present in the perineurium to inhibit the axons from leaving the
nerve

22. REGENERATION OF AXONS IN THE CNS
 Central axons may not be as good at regeneration as peripheral axons
 The regeneration process is aborted by:
1. Failure of oligodendrocytes to serve in the same manner as schwann cells
2. Laying down of scar tissue by the active astrocytes
3. Absence of nerve growth factors in the CNS
4. Neuroglial cells may produce nerve growth-inhibiting factors

24. REFERENCES
 Clinical neuroanatomy, 7/E snell
 Essentials of medical physiology, 3/E mahapatra
 Principles of neural science, 5/E kandel ER, schwartz JH, jessell TM (editors)

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